What is Allergy?
An allergy is when your pet's immune system has an over-reaction to what would normally be considered a harmless substance - this substance is known as an allergen. Common allergens can include things like:
- house dust
- food
- grass pollen
- weed pollen
- fleas
- mould
Instead of ignoring the allergen, your pet's immune system sees it as a threat and initiates the bodies defence response - inflammation - and this results in itching.
Increased itching often causes animals to scratch and lick more, which in turn can cause secondary skin infections, particularly around the paws, face, ears and abdomen.
The Allergic Response
Allergens can enter the body through the skin, the eyes or the mouth. Upon doing so, your pet's immune system is primed to trigger an antibody response which causes the release of histamine. Very quickly, these substances cause swelling, inflammation and itching of the surrounding tissues which usually causes your pet to scratch and lick the skin. 
Did you know that pet’s allergy is a vicious cycle?
When your pet has an allergy to food, fleas, or something in the environment, there are several things that happen within the body. Scratching, licking and chewing results from exposure to allergy “triggers” and a frustrating cycle of itching starts that often continues and may get progressively worse. Your pet may continuously scratch, bite, chew or lick specific areas. A red rash or hot spots on the skin may appear, along with skin inflammation.
Early allergic itching, while annoying and bothersome, may be sporadic and mild. But left untreated and with ongoing exposure to allergens that trigger it, this itching quickly progresses and becomes more severe and persistent—interfering with everyday activities and potentially leading to other health problems, such as skin and ear bacterial/yeast infections. So, it’s best to control allergy right from the start—before this vicious cycle begins—and additional health issues arise that are difficult to manage and further add to your pet’s discomfort.
Unfortunately many of these cases are not diagnosed and treated since symptoms can be mistaken with behavioural acts. Most common symptoms are itching and scratching. Licking and biting paws, over-grooming, rubbing their face against the floor or furniture are also very common. Many pet owners may assume this behaviour is normal for their pet and as such merely put up with it. However, such behaviours are not usually normal and as such, it is important to know how to identify if your dog or cat may be allergic. 
The Allergy Itch Threshold
When we talk about allergy, the itch threshold is used to describe the point at which the response to the allergen(s) is significant enough to cause symptoms such as itching.
How quickly this threshold is reached will vary from patient to patient. For some, exposure to a small amount of a single allergen such as house dust may be enough to trigger their symptoms. For another, it may be the cumulative effect of a number of allergens that results in symptoms occurring. Pet's with allergies will always be prone to more flare-ups as they sit closer to the threshold than dogs without them.
When managing a pet with allergies, the goal is to keep them below their individual itch threshold for as long as possible. By understanding which allergens your pet is allergic to, you may be able to manage their environment or take measures to help ensure exposure to the allergens is reduced.
Itch Severity
When caring for a pet with allergy, it is useful to identify and score the itch level. We can use a scale that grades how sever the itching may be. To use the scale, you simply record where you feel your pet sits on the spectrum of itchiness on any given day. It can then be compared to previous and future scores so that you can gauge how successfully your pet is being managed.
Grading the itch is extremely useful as you are able to learn what is normal for your pet. Changes from this 'normal' can be used to predict flare-ups, monitor progress and check their response to treatment. Spotting changes in their itch level, alongside other tell-tale signs and symptoms for your pet that their skin may be flaring up again, allows you to help bring their condition back under control.
An example of an itch scale you can use to grade your pet's itch can be seen below.
You can use an itch tracker such as this to keep record of your pet's itch severity week-by-week.
